Flotation of oxide ore minerals



Patented July 11, 1939 UNITED STATES PATENT. creme FLOTATION OF OREMINERALS Mikael Vogel-Jorgensen,

Frederiksberg, near Copenhagen, Denmark, assignor to Separation ProcessCompany, a corporation of Delaware No Drawing.

Application June 30, 1937, Serial No. 151,203. In Great Britain July 17,1936 5 Claims.

argillaceous limestones, marls and chalks, to produce concentratesuseful in the manufacture of Portland cements, but it will be understoodthat it is of broader scope.

In general, the invention has to do with the utilization of talloel, awaste product derived from the black liquor soap of the sulphate processfor the manufacture of cellulose and paper. Talloel, as referred toherein, is the refined product obtained when the black liquor soap,which floats on the black liquor, has been removed by skimming and isthen treated with a mineral acid, usually sulphuric acid, and refined toremove ligneous and other insoluble material, and should not be confusedwith black liquor soap itself, which contains ligneous matter and otherimpurities which render it unsatisfactory as a flotation reagent. Thetalloel is saponified and preferably clarified of any insoluble matter,and may be employed in dilute solutions in water. The phrase saponifiedtalloel throughout the specification and claims is limited to thedefinition of a'reagent which has been saponifled prior to its additionto the water of a flotation pulp, to distinguish the reagent fromtalloel possibly at least partially saponifled by soap-forming alkaliespresent in the'pulp water, Talloel, separately with fuel oil, has beenused as a fiotation reagent, but lacks many of the advantageousproperties of saponifled talloel and is not its equivalent in eitherhandling or flotation characteristics, but is' similar to the high titrefatty acids in handling characteristics and collccting power, althoughoi! greater frothing power. The 'saponified talloel has selectivecollecting qualities for the oxide mineral-grains and also frothingcharacteristics, both of which may be controlled-or modified to-satisfythe conditions of a specific flotationrgjilp and circuit. The collectingpower per unit weight of reagent and material can'be increasgfid by theuse of increasing quantities of fatty acids,' preferably saponidied withthe talloel, the mixture having lower frothing characteristics than anequivalent weight of saponifled talloel. The frothing characteristlcsmay be ubstantially l'gqllgegl by incorporating increasing quantities offuel oil with the saponified talloel without apparent decrease incollecting power in quantities not exceeding equal proportions by,weight of fuel oil and raw talloel, low proportions of fuel oilslightly increasing collecting power, but reducing selectivity. Bymixing the fuel oil with the raw talloel before the saponifying reagentis added, as will be described more fully hereinafter, the

product is apparently completely soluble in water, or at least forms aclear aqueous dispersion that is stable at all working dilutions andtemperatures. Some of the "soluble mineral oils and soluble vegetableoils may be substituted for fuel oil, but are less satisfactory as theyare more expensive, many must be emulsified and aqueous dispersions ofthe mixtures are unstable and make operation erratic.

Among the purposes of the invention are to provide a low cost but highlyselective collecting reagent; to extend the practical use of flotationfor the economical recovery of oxide ore minerals of low commercialvalue, and to permit the recovery of useful concentrates from slimypulps which do not react successfully to froth flotation with the knowncollectors. Among the advantages of. 'saponified talloel are first, thatit can be diluted in water to any convenient degree to make possiblelight and uniform stage oiling; second. it is completely stable at allworking temperatures and is quickly dispersed even in ice water; third,it takes effect quickly and its action ceases quickly, i. e., it issensitive; fourth, the coating of the oxide mineral grains is light,thereby avoiding heavy flocculation with consequent trapping of finegangue particles, and fifth, it is highly selective. These advantagesextend the practical use of flotation to the. recovery of the valuablecontent of slimes, such as those described later, which are not amenableto flotation to produce concentrates of commercial grades, with theusual collectors, such as the fatty acids, resin acids, soaps oremulsions, or mixtures thereof. The light coating may readily be atleast partially removed by washing, thereby promoting rapid thickening.

Froth flotation processes have been employed successfullyheretofore forthe purpose of deriving satisfactory cement raw material mixtures, orlime components thereof, from inferior argillaceous limestones, marls orchalks, containing excessive quantities, or undesirable proportions,oi'one or more of the argillaceous constituents, usually aluminacompounds and crystalline silica. It is among the purposes of theinvention to reduce the cost of these processes and to extend thepractical or economical utility of fiotation to the treatment ofmaterials that cannot be separated readily or practically with the knownreagents. The use of cold water is not the least of these economiessince not only is the cost of heating the relatively enormous watervolumes of a classification, flotation and thickening circuit eliminatedbut also classification and thickening are not unbalanced by thecurrents of warm water.

In many of the materials of the types described, the component mineralsare naturally so fine, or must be reduced to such fineness to free themineral bonds, that the resulting pulp is a slime, or the proportion ofslime is so large that it may not be wasted. In addition to the finelydivided calcite, the slimes almost always include a wide variety of clayminerals, micaceous matter and crystalline silica, which tend toflocculate naturally in a flotation pulp, many of the mineral particlesbeing colloidal or having colloidal behavior. The low commercial valueof Portland cement, precludes the use of dispersing reagents prior tothe introduction of the usual collectors, and dispersers are not alwayseffective in view of the variety of classes of mineral compounds. Theusual fatty and resin acids are ineffective as their relatively highlycollecting power and poor selectivity produces heavy flocculation andconsequent trapping of the fine gangue minerals. Further, these reagentscannot be uni- -formly and quickly dispersed in coldwater, some of themdispersing slowly if at all.

Solutions of the fatty or resin acids, or mixtures thereof, in mineraloils likewise cause overoiling, the heavy flocculation producinglow-grade concentrates, and are almost as difiicult to disperse in thepulp. The usual soaps produce lowgrade concentrates but their principaldisadvantage is their exceptionally poor selectivity. Emulsions of fattyand resin acids may be dispersed readily but produce matted froths oflower grade than saponified talloel, the froths being diificult to breakdown, aggravating difficulties in thickening, forming excessive andheavy scum on the thickeners and more dilute thickener underfiow.

The reagent is prepared by saponifying the refined talloel with thecustomary reagents such as caustic soda, potash or ammonium hydroxide.Between 10 and 14% of caustic soda on the weight of the talloel, or theequivalent of another saponifying reagent, may be required dependingupon the acid value of the available talloel. Incomplete saponificationresults in a mixture comparable to an unstable fatty acid emulsion withrespect to its handling characteristics, but is more selective inflotation. Saponification is accelerated by slow boiling and stirringthe mixture, satisfactory results being had when the lumps havedisappeared, but it is preferable to add the causticuntil the mixture isalkaline within' a range between pH 9 and 9.5, particularly for calciteconcentration. Any insoluble matter canbe removed by allowing themixture to settle for several days, when the supernatant liqfuidomay'bedrawn off. .At least partial dilution withsuwater "acceleratesclarification. The reagent may less conveniently be clarified byfiltration. To obtain'a maximum uniformity in dispersing the'reagei'itin the pulp and to permit closely controlled light stage oiling, thereagent referably'used'in 5% to 20% dilution in waterfalthough'ot'herjdilutions may be employed, the finer pulps-responding moresatisfactorily to the more dilute solutions. The use of saponifiedtalloel has no marked effect on the alkalinity of pulps of the typesdescribed, which remain in. the normal range between pH 7.6 and 7.8, thealkalinity of limestone pulps being naturally buffered by dissolvedcarbon dioxide.

When the pulp does not contain excessive quantities of the finer slimes,the collecting power can be increased and the frothing characteristicsreduced and controlled, whereby flotation is more rapid, by the use ofincreasing quantities of fuel oil. By reducing the frothingcharacteristics, frothing reagents may be employed to control thebalance of stage oiling circuits. saponified talloel is insoluble infuel oil, but if prior to saponification, in the manner described above,the fuel oil is mixed with the raw talloel and the caustic is addedafterward, the composition is apparently completely soluble in water oris possibly a clear aqueous disperson stable and capable of dilution toany degree at any working temperature. An excess of caustic soda isrequired. For talloel requiring 12% caustic soda for completesaponification, a mixture of equal parts of talloel and fuel oil byweight requires a total of 20% caustic on the weight of the mixture toproduce a clear or stable solution. It is to be understood that the bestresults are obtained by proportioning the relative quantities of fueloil with relation to the fineness of the slimes, partial desliming orincreasing grain sizes permitting satisfactory use of increasingquantities. Increasing proportions of fuel oil increase the collectingpower, but decrease the selectivity, and no appreciable loss incollecting power is apparent when the proportion of fuel oil does notexceed that of the talloel, but beyond this proportion collecting powerdrops rapidly. Frothing characteristics, desirable with fine pulp butundesirable with coarse, particularly in stage oiling circuits, decreaseas the proportion of fuel oil is increased. While the use of saponifiedmixtures of talloel and fuel oil is included within the broad scope ofthe invention, this specific improvement is not claimed herein, assaponified talloel and fuel oil mixtures, which are miscible with water,are the invention of Robert C. Ried and are described and claimed in hisco-pending application, Serial No. 163,307, filed September 10, 1937.

In pulps in which the finer slimes are not abundant, substantiallyincreased collecting power is desirable to decrease the pulp dilutionsand the flotation time, to limit the amount of flotation equipmentnecessary. This is accomplished by incorporating, as a part of thereagent, quantities of fatty acids, increasing quantities givingfavorable results as the relative coarseness of the mineral grainsincreases. The increasing additions of the fatty acids likewise reducethe frothing characteristics, but to a lesser degree than fuel oils, butalso make it possible to add quantities of the common frothing agents,such as cresylic acid or alcohol' frother identified hereinafter,-afeature of especial utility in'stage oiling circuits as it provides foraccurate control of each stage. Conversely, with an appropriate pulp anda stage oiling circuit, a low proportion of fatty acid results inexcessive frothingin the first stages and too little frothing in thelater stages.

The fatty acid and talloel are first mixed, then saponified andclarified in the manner described above. The saponified mixture iscompletely soluble and may be used in any convenient dilution, formng anexcellent collector 'in cold water, in which the selective effect of thesaponified talloel is marked in relatively coarse pulp, and provided theproportion of fatty acid does not exceed that of the talloel. Further,excesses of some fatty acids, above an equal proportion, andparticularly fish oil fatty acid, usually produce an unstable and lumpymixture instead of a clear solution.

For a better understanding of the invention eference is made to thefollowing examples. To interpret the results properly, it should beborne in mind that, in a Portland cement raw material of concentratesufilciently high that only a part of the cement raw materials need betreated and the concentrates mixed with the remainder, a

natural material or both.

First example To illustrate the concentration of calcite from a fineslime, for purposes of cement manufacture, by the use of saponifiedtalloel, the material treated'was an argillaceous marl. Natural mineralparticle sizes were so fine that extreme grindrecovery being 90% ing wasrequired to free the constituents to a degree that a useful grade ofconcentrate could be obtained. The marl was ground in closed circuit,the classified product, forming the flotation pulp, being substantiallyall minus 325 mesh sieve and about minus 10 microns.

The calcium carbonate content was 68.5%, by titration. The pulp dilutionwas 15% on a dry solids basis. A 10% solution in water of saponifledtalloel was used in the rougher concen-- tration and produced aconcentrate of 77.6% calcium carbonate, the calcium carbonate weightReagent consumption was 1.54 pounds of saponified talloel a tonof drysolids and the flotation time was 8 minutes.

The same material with oleic acid and with cresylic acid, as a frother,produced a concentrate of 74% calcium carbonate, approximately 2% belowthe necessary cement raw material composition. The reagent consumptionwas higher, 4.4 pounds of oleic acid being required, and the flotationtime was increased to 10 minutes.

Second example To illustrate a so-called pulp, and the use of saponifiedmixture of talloel and fuel oil, in which the fuel oil was employedprincipally to reduce frothing, for control in a stage oiling circuit,the material used as the flotation feed wasa metamorphosedmicaceouslimes'tone, deficient in calcite and excessive in alumina andsilica. It was-normal tube'mill slurry 'of regular cement milloperation. The calcium carbonate content was 64%. The objective was toraise 'the concentrate to cementrawf-material composition, namely about76% calcium carbonate. The physical analysis was as follows:

3.2% plus 100 mesh 20.5% minus 100 plus 200 mesh 18.9% minus 200 plus325 mesh 57.4% minus 325 mesh 25.0% minus 10 microns The reagent usedwas a saponified mixture of 60% refined talloel and 40% fuel oil,saponified with 20% NaOH on the weight of the mixture and diluted to 3%solution in water for convenience in handling and accuracy of control.

' The pulp in the first rougher cell was diluted to 18% dry solids incold water. The grade of the concentrate of the first rougher cell was76% calcium carbonate, the total weight recovery was 72.6%, the calciumcarbonate recovery was 86.2%,

without cleaning or skimming. Flotation time was 5.25 minutes. R eagentconsumption was 0.856 pound of the saponified mixture and 0.0594 poundof alcohol frother comprising a mixture of branched and straight chainaliphatic monohydric alcohols boiling between about 152 C. and about 162C. obtainable along with methanol *fby the catalytic hydrogenization ofcarbon oxides.

Third example To illustrate a so-called "coarse" pulp and the use of asaponified mixture of talloel-and fish oil fatty acid, the materialtreated was similar to that of the second example, taken from the samequarry but of better grade. It was also normal tube mill slurry, ofregular cement mill operation, but somewhat finer. The calcium carbonatecontent was 72.7%. The physical analysis was as follows:

2.7% plus 100 mesh 20.4% minus 100 plus 200 mesh 16.9% minus 200 plus325 mesh 60.0% minus 325 mesh 25.0% minus 10 microns The reagent usedwas prepared from a mixture of equal parts of raw talloel and high titrefish oil fatty acid of 75 to 78% acid value, saponified by 12% NaOH onthe total weight of the mixture, clarified as described above, anddiluted for accuracy in-control to 3% solution in water. The pulp in thefirst rougher cell was diluted in cold water to18% dry solids. Theobjective was to raise the grade of the concentrate so that only a partof the material mixture had to be treated by flotation. The firstrougher cell concentrate was 86.7% CaCOa, without skimming and withoutcleaning, the total weight recovery was 85.5% and the calcium carbonaterecovery was 98.7%. The

- weight loss in calcite in the rejects of the first rougher operationwas 1.3%. The flotation time in the first rougher cell was 3% minutes.Re-- agent consumption was 0.785 pound a ton of dry .feed.Significantfifeatures of these results are that the fine andthecoarsecalcite grains were collected together, reagent consumption waslow,

flotation was rapid and the calcite loss was neglislble.

A check test with a mixure of equal parts of raw talloel and fish oilfatty acid failed to produce a substantial improvement in the grade ofthe flotation celllfeed, due principally to the failure to obtaindispersion in cold water.

. Fourth example Material substantially similar to the second and thirdexamples in fineness and composition was treated with a saponifiedmixture of talloel and oleic acid, in the same manner. The feed had acalcium carbonate content of 71.6%. The reagent was a mixture of 60%talloel and 40% oleic acid, saponified with 12% NaOH, on the totalweight of the mixture, which was diluted to 3% so ution in water. Thecalcium carbonate content of the concentrate was 84%, total weightrecovery 83.9%, calcium carbonate weight recovery 98.2%, and the rejectwas 16.1% weight with l a grade of 0.8% calcium carbonate. Reagentconsumption was 0.8 pound of the mixture a ton of dry feed. Theflotation time was 4 minutes.

In all of the foregoing discussion, the term coarse, as applied to someof the pulps referred to, is relative, and it should be understood thatthese pulps are slimes, or contain an abundance thereof, within themeaning of the term slimes in the art of flotation. Saponified talloelhas a marked tendency to disperse naturally flocculated pulps andsatisfactory grades of concentrates can accordingly, be produced withoutthe use of dispersing agents. However, the usual dispersing agents canbe used with the present reagent to complete dispersion to improve thegrade of the concentrates, but the low commercial value of theconcentrates, with which this invention is particularly concerned,ordinarily makes the cost of dispersers prohibitive. Further, andalthough the invention opens a new field of utility for flotation in thedifferential separation of slimes, it should also be realized that it isnot so limited, but that the selective characteristics and low costmakes the reagent an excellent collector for use in normal de-slimedpulps.

.I claim:

1. 'Ifhe method of concentrating oxide ore min-= erals by frothflotation which comprises intro 'ducing substantially completelypre-saponified completely pre-saponified mixture of acid-refined talloeland a. fatty acid in an aqueous oxide ore mineral pulp and agitating andaerating the pulp in the presence of said saponifled mixture.

3. The method of concentrating calcite by froth flotation from siliceousgangue minerals which comprises introducing a clarified aqueous solutionof a pre-saponified acid-refined talloel in an aqueous pulp containingcalcite and agitating and aerating the pulp in the presence of saidsaponified talloel.

4. The method of concentrating calcite by froth flotation from siliceousgangue minerals which comprises introducing a pre-saponifled mixture ofacid-refined talloel and a fatty acid in an aqueous pulp containingcalcite and agitating and aerting the pulp in the presence of saidsaponified mixture.

5. The method of concentrating calcite by froth flotation from siliceousgangue minerals in a stage oiling circuit which comprises introducing anaqueous solution of a pre-saponified mixture of acid-refined talloel anda fatty acid in an aqueous pulp containing calcite, agitating andaerating the pulp in the presence of the mixture, and controllingfrothing characteristics of the stages by additions of a separateirothing agent.

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